A USA TODAY/Gallup Poll taken of 488 registered voters over the weekend showed 53 percent of respondents hadn't heard of Ryan or didn't know enough about him to form an opinion.

Ryan had a 27 percent favorability rating in that poll, with 21 percent unfavorable. The survey, which had a margin of error of plus-or-minus 6 percentage points, said 39 percent viewed Romney's selection of Ryan as a good choice, with 45 percent rating it "only fair" or "poor." USA Today reported the results as "the most tepid reception for a running mate" since Dan Quayle joined the GOP ticket in 1988.

A poll from Reuters and Ipsos found that although 80 percent of respondents had heard of Ryan, just 35 percent said they were familiar with him.

Ryan trailed incumbent Vice President Joe Biden 44-29 when respondents were asked which candidate was more qualified to serve as president if necessary. The poll surveyed 508 registered voters between Aug. 11 and Aug. 13 -- including a day before the Ryan pick was announced; the margin of error was plus-or-minus 5.1 percentage points.